In a typical operational transconductance amplifier, the bias current must increase with increasing temperature to maintain a constant small signal bandwidth. Because of this, it is typical to employ a bias circuit that provides a larger bias current at higher temperatures. This allows a lower bias current at room temperature while maintaining performance at high temperatures.
This positive slope of the bias current versus temperature may be as much as 85% of a true proportional to absolute temperature current. The slope is typically controlled by adding a PTAT current to a current that is constant over temperature. An issue typically associated with this type of biasing is that the large signal behavior of the amplifier under slew rate limited conditions degrades at low temperatures. This is because the available charging current is lower. With an 85% PTAT slope, the current at −40° C. can be 22% lower than at +40° C.
In view of the foregoing, it may be useful to provide methods and systems that facilitate non-linear temperature dependence for CMOS operational transconductance amplifiers. Similar provision of methods and systems for other technologies, such as bipolar or other MOSFET (e.g. NMOS or PMOS) circuits may also be useful.
The foregoing examples of the related art and limitations related therewith are intended to be illustrative and not exclusive. Other limitations of the related art will become apparent to those of skill in the art upon a reading of the specification and a study of the drawings. Additionally, limitations and disadvantages of the related art may become apparent from review of other related art itself.